1. Field of the invention
This invention relates to bags or sacks for vacuum cleaners, especially of the type used for large vacuum cleaners or for vacuum cleaners for the industry.
2. Description of the prior art
When dust is sucked into a vacuum cleaner of conventional type the dust-laden air passes into the vacuum cleaner and through a dust-collecting bag or sack, and the cleaned air passes through the walls of the bag or the sack and out of the vacuum cleaner. It is a disadvantage of conventional dust-collecting bags or sacks that their walls are rapidly becoming clogged by dust and that the pressure drop across the walls of the bag or the sack soon becomes so high that the suction effect rapidly decreases and the bag or the sack must be replaced. However, only a small proportion of the volume of the bag or the sack will then usually be filled with dust, and, accordingly, the conventional dust-collecting bags or sacks are poorly utilized with regard to their total volume.
Previously, permanent dust-collecting bags of cloth were used in the conventional household vacuum cleaners. When the user noticed that the suction effect became too poor, the suction head had to be removed from the vacuum cleaner, the bag had to be loosened, the dust had to be shaken out of the bag and the bag had to be thoroughly shaken in order to remove the absorbed and obstructing dust in the bag walls. This was an uncomfortable and laborious operation. In vacuum cleaners of the more modern type disposable insert bags of porous paper of special grades are used which are thrown away when the bag walls have become so clogged by dust that the suction effect ceases or is strongly reduced.
There is a further problem connected with vacuum cleaners used in the industry that the dust sucked in may be very dense and the necessary suction pressures so high that the dust-collecting paper bags used may easily tear apart due to the heavy strain to which the bags are exposed. Because a relatively unhindered passage of air through the walls of the dust-collecting bags is necessary in order to obtain a reasonable service life and a reasonable amount of dust sucked into the bag before the bag has to be replaced, such dust-collecting bags may necessarily not consist of strong paper of low porosity or of several layers of paper because the pressure drop across a such bag would then rapidly increase leading to reduced suction effect. Also with the dust-collecting bags used in vacuum cleaners for the industry the volume filled with dust will be relatively low compared with the total internal volume of the bag before the suction effect has been reduced so strongly that the bag must be replaced.
Accordingly, there is great demand for an improved dust-collecting bag for use in vacuum cleaners, especially in vacuum cleaners for the industry, which will not be clogged by dust before a substantial portion of the internal volume of the bag has become filled with dust, which has a sufficient mechanical strength to be able to withstand handling while being inserted into and removed from the vacuum cleaners and to contain large amounts by weight of dust with regard to the internal volume of the bag without tearing thereof, and which during use and until it has been essentially filled with dust does not cause the pressure drop across its walls to increase substantially compared with the pressure drop when starting the suction of the dust.